1. Field of the Invention
The present invention relates to an air temperature control system for a vehicle for controlling a cooling unit cooling the inside of the vehicle or a heating unit heating the inside of the vehicle.
2. Description of Related Art
An air temperature control system for a vehicle for controlling air conditioning or heating units in order to cool the vehicle's rear seat area by means of a rear cooling unit and to heat the rear seat area by means of a rear heating unit is disclosed in Japanese Patent Number B2 258126. More specifically, a required quantity of heat Q.sup.R is determined for maintaining the rear seat air temperature at a predetermined rear seat air temperature. When the required quantity of heat Q.sup.R is negative, the rear cooling unit starts cooling the rear seat air with the rear heating unit turned off. When the required quantity of heat Q.sup.R is positive, the rear heating unit starts heating with the rear cooling unit turned off.
When cooling the rear seat air, a required air quantity WRC to the rear seat is determined based on the deviation between the rear seat air temperature and the predetermined rear seat air temperature, and a target blowout temperature TAO.sup.4 necessary for obtaining the above-mentioned required quantity of heat Q.sup.R under the required air quantity WRC is calculated. Accordingly, a coolant valve for controlling the coolant flow to a rear evaporator is turned on and off to obtain the target blowout temperature TAO.sup.R without frosting the rear evaporator.
In addition, when heating the rear seat area, the required air quantity WRH is determined based on a deviation between the rear seat air temperature and the determined rear seat air temperature, and the target blowout temperature TAO.sup.R, necessary for obtaining the required quantity of heat Q.sup.R under the required air quantity WRH, is calculated. Accordingly, a water valve for controlling the flow of warm water to a rear heater core in the rear heating unit is turned on and off to obtain the target blowout temperature TAO.sup.R.
However, in the aforementioned air conditioning unit, when the outside air temperature is in an intermediate region, between 10 and 20.degree. C., for example, a problem occurs. That is, when cooling the rear seat, sometimes the target blowout temperature TAO.sup.R is over, e.g., 15.degree. C. At this time, after wind airflow based on the temperature is generated by the rear evaporator, a foul smell is emitted due to the dust and mold in the rear evaporator and oxide caused by the corrosion of the rear evaporator, thereby giving passengers in the vehicle compartment an unpleasant feeling. Needless to say, this kind of problem also occurs when providing a cooling unit at the front seat area.
Further, when heating the rear seat, the target blowout temperature TAO.sup.R sometimes falls below the inlet temperature of the rear heating unit. However, since the rear heater core in the rear heating unit produces airflow at temperature in excess of the inlet temperature, the airflow at a temperature under the inlet temperature cannot be produced by the rear heating unit. This kind of problem also occurs when providing the heating unit at the front seat area.